netdev - Re: [B.A.T.M.A.N.] ibss.c backtrace when batman-adv adds wireless interface

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Date:	Wed, 03 Feb 2016 18:09:40 +0100
From:	Sven Eckelmann <sven@...fation.org>
To:	b.a.t.m.a.n@...ts.open-mesh.org
Cc:	Johannes Berg <johannes@...solutions.net>,
	Josh Boyer <jwboyer@...oraproject.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	Marek Lindner <mareklindner@...mailbox.ch>,
	Kalle Valo <kvalo@...eaurora.org>,
	Simon Wunderlich <sw@...onwunderlich.de>,
	netdev <netdev@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: Re: [B.A.T.M.A.N.] ibss.c backtrace when batman-adv adds wireless interface

On Wednesday 03 February 2016 16:41:30 Johannes Berg wrote:
> On Wed, 2016-02-03 at 10:26 -0500, Josh Boyer wrote:
> > On Wed, Feb 3, 2016 at 10:24 AM, Josh Boyer <jwboyer@...oraproject.or
> > g> wrote:
> > > Hi All,
> > > 
> > > We've had a user report the backtrace below when loading batman-adv 
> > > on
> > > his machine.  It looks like the cfg80211 layer is complaining about
> > > a
> > > null bss returned, but I cannot tell if the rtlwifi driver or
> > > batman-adv is in error here.
> > > 
> > > Thoughts?
> > 
> > Sorry, forgot to include the link to the actual bug report:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=1304428
> > 
> > Reporter says this is new with 4.3.y and did not happen on e.g.
> > 4.2.8.
> > 
> 
> AFAICT this should be a driver (or perhaps mac80211) issue, but I don't
> see any information about the driver used.

It doesn't really look like it is batman-adv specific. batman-adv also doesn't
be active because the message "batman_adv: bat0: Adding interface: " is
missing.

batman-adv is also not responsible for the underlying device. So it will not
join IBSS and thus should not trigger the "wlp0s26u1u4: Selected IBSS BSSID"
seen in the log.

But that said, I already saw weirder things happen because of memory
corruptions. So I will not say that batman-adv cannot be the culprit but right
now I don't see how.

The user can also try (when he thinks that batman-adv is to blame) to bisect
the batman-adv versions via the git of the out-of-tree module [1]. The version [2]
from 4.1 should be roughly v2015.0 (b6ff92aa334083dee8a1f5f0c5aa0f7c4c2584cf),
v4.2 should be v2015.1 (95b64b1cef38340f48f4eba99689e0fb1feddcd0) and v4.3 should
not be newer than v2015.2 (e25bd38b0f8b4aeca85ef24884fa5eadd6270709). So bisecting
between b6ff92aa334083dee8a1f5f0c5aa0f7c4c2584cf and
e25bd38b0f8b4aeca85ef24884fa5eadd6270709 (~6 steps) should cover it. I personally
would recommend to start on 4.2.8 with v2015.2
(e25bd38b0f8b4aeca85ef24884fa5eadd6270709)

Kind regards,
	Sven	

[1] https://git.open-mesh.org/batman-adv.git
[2] https://www.open-mesh.org/projects/open-mesh/wiki/Download#batman-adv-in-the-Linux-tree

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